Metal films are used widely within semiconductor integrated circuits to make contact to and between semiconductor devices (i.e., metal interconnects). Because of the high densities required for modern integrated circuits, the lateral dimensions of interconnects, as well as the lateral dimensions between interconnects, have shrunk to such a level that a single defect can destroy an entire wafer die by shorting a junction region or open-circuiting a gate electrode of an essential semiconductor device. Defect reduction within interconnect metal films, therefore, is an ever-present goal of the semiconductor industry that increases in importance with each generation of higher density integrated circuits.
Interconnect metal films typically are deposited via physical vapor deposition and more recently via high density plasma (HDP) deposition, within a plasma chamber. In both processes, a target of to-be-deposited material (e.g., the metal comprising the interconnect) is sputtered through energetic ion bombardment that dislodges atoms from the target. The dislodged atoms travel to a substrate disposed below the target and form a metal film thereon. The metal film is patterned to form the interconnect.
For HDP deposition, in addition to the target, a coil is provided between the target and the substrate. The coil's primary role is to increase the plasma density, i.e., ionization fraction, and thereby create conditions to ionize target atoms sputtered from the target. Ionized target particles will, under the influence of an electric field applied between the target and the substrate, strike the substrate substantially perpendicular to the target face and substantially perpendicular to any feature base present on the substrate (e.g., allowing for improved filling of vias and other surface features). Where the coil is located internally of the chamber, the coil itself is sputtered, and dislodged coil atoms travel to the substrate disposed below the coil and deposit thereon. Sputtered coil atoms predominantly coat the substrate near its edges and, where the target atoms create a center thick film on the wafer, enhance the overall thickness uniformity of the material layer formed on the substrate. The material properties of an HDP coil therefore play an important role in overall deposited film quality.
As described in parent applications, U.S. Ser. No. 08/979,192, filed Nov. 26, 1997 and U.S. Ser. No. 09/272,974, filed Mar. 18, 1999, both aluminum target manufacturers and copper target manufacturers conventionally focus on the purity of sputtering targets to reduce defect densities or to otherwise affect deposition of high quality metal films. Similar emphasis is placed on the purity of coils employed in HDP deposition chambers (e.g., HDP deposition chambers typically employ a target and a coil having similar purity levels). However, despite high purity levels for both targets and coils, the defect densities of conventional HDP deposited metal films remain high.
Accordingly, a need exists for a coil for use within an HDP deposition chamber that produces metal films having reduced defect densities.